The present invention relates to radio frequency (RF) coverage planning, and more specifically, to methods for visualizing RF coverage.
RF coverage planning assists the RF engineer in answering the question, where do I need to put antennas to provide a specified service level over a given area, or to answer the corollary question, what will my coverage be if I put antennas in the following locations?
One skilled in the art of RF engineering can perform calculations and make coverage predictions. These predictions typically require information along the following lines to be available: radio characteristics such as transmit power and receive sensitivity, antenna radiation characteristics, transmission lines, and the medium through which the coverage must be planned.
In a method typical of the prior art in displaying coverage based on antenna characteristics, the engineer first obtains antenna pattern information. This may be obtained from measurements, by modeling the antenna, or may be provided by antenna suppliers. Such antenna information is typically presented as a series of 2 dimensional plots in logarithmic units such as dBi (decibels above isotropic) or dBd (decibels above dipole). FIG. 1 shows typical antenna plots as known to the art. Two pattern plots called “Azimuth” on the left and “Elevation” (or horizontal and vertical) on the right are shown for various frequencies, representing two planes of the complete 3 dimensional antenna pattern. As is common to the antenna arts, these plots are dimensioned in logarithmic units, not linear units. In the plots of FIG. 1, the outer circle is the 0 dB reference line. The circles labeled 10 are 10 dB below the 0 dB reference, a factor of 10 decrease in power. The circles labeled 20 are 20 dB below the 0 dB reference, a factor of 100 decrease in power.
Based on the two dimensional Azimuth plot shown in FIG. 1, the engineer can obtain the maximum antenna gain, the direction of maximum gain, and the gain relative to the maximum in any horizontal direction. Similarly, the two dimensional Vertical plot carries this same information for the vertical direction.
Using such gain plots, the engineer defines a coverage area. This coverage area is typically described based on the angles at which the antenna pattern is 3 dB below the maximum, representing a factor of 2, or a 50% reduction in power. These angles are referred to as the “−3 dB beamwidth” and the area contained in this beamwidth is referred to as the “Coverage Area.”
A two dimensional graphic representation of the coverage area is prepared based on antenna and radio characteristics. This may be formed using polygons or circles, or a line showing maximum range of coverage. This two dimensional graphic representation is presented along with other two dimensional graphics such as floor plans or maps to show the coverage area for planning purposes or network monitoring. Such a display as known to the art is shown as FIG. 2.
This method of visualization has a number of problems. The antenna coverage as described does not accurately represent the full three dimensional coverage of the antenna system. When used for planning purposes, this can lead to unexpected coverage loss when the vertical or elevation pattern of the antenna is important. When used for monitoring, the lack of full three dimensional antenna pattern visualization can lead to difficulties in solving coverage problems. These occur, for example, when the antennas being deployed are in different vertical planes than the devices they will be servicing, such as when antennas are placed high on poles or towers, or antenna coverage is to be calculated for an area with a range of vertical positions, such as the interior of an arena with seats at many different levels.
When prepared according to the process described, coverage visualization is not directly scalable when viewed on maps or charts. This is because antenna pattern information is traditionally and typically presented in logarithmic units (e.g. dBi) as shown in FIG. 1, while maps and charts are in linear units (meters or feet). Thus, if radio, antenna, or other aspects of the coverage model change, the graphical representation (coverage model) must be completely recalculated and redrawn.